This invention relates generally to gas turbine engines and more particularly to combustor dome plates used in such engines.
A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and ignited for generating hot combustion gases. These gases flow downstream to one or more turbines that extract energy therefrom to power the compressor and provide useful work such as powering an aircraft in flight. Combustors used in aircraft engines typically include inner and outer combustor liners to protect the surrounding engine components from the intense heat generated by the combustion process. The combustor liners are joined at their upstream ends to a dome assembly. The dome assembly includes an annular dome plate and a plurality of circumferentially spaced swirler assemblies mounted therein for introducing the fuel/air mixture to the combustion chamber.
One conventional dome assembly includes a dome plate having a plurality of openings, referred to herein as eyelets, formed therein for receiving the swirler assemblies. The dome assembly further includes a baffle extending downstream from each swirler assembly for shielding the dome plate from the hot combustion gases of the combustion chamber. The baffles are thus subject to intense heat and must be cooled to extend the life thereof. Baffle cooling is accomplished by impingement-type cooling holes formed in the dome plate so as to cause compressed air to impinge against the upstream side of the baffles. This impingement air subsequently xe2x80x9cspills offxe2x80x9d the baffles and flows downstream so as to cool the outer and inner liners. However, impingement air tends not to xe2x80x9cspill offxe2x80x9d in the gaps formed between adjacent baffles. Thus, additional cooling holes, typically referred to as blow-off holes, are formed in the dome plate in locations aligned with the baffle gaps. The blow-off holes thus direct air flow onto the areas of the inner liner that are circumferentially aligned with the baffle gaps, areas that would otherwise not be cooled because of the lack of impingement air spill off.
As used herein, the term xe2x80x9ceyeletxe2x80x9d refers to particularly shaped opening formed in a dome plate. A dome plate having such an eyelet is shown in FIG. 6 of U.S. Pat. No. 5,117,637 issued Jun. 2, 1992 to Stephen J. Howell et al. As can be seen in the Howell et al. patent, two characteristics of an eyeletted dome plate are that the corners between the eyelets and the outer and inner edges of the dome plate define sharp, compound radii, and the circumference of each eyelet defines an axially facing lip.
While eyeletted dome plates generally provided excellent performance, they do tend to be relatively expensive to manufacture. For example, because of the sharp compound radii corners that result from formed eyelets, the blow-off holes must be accurately positioned with respect to the inner liner. Otherwise, the cooling air flow issued from the blow-off holes will jet into and disrupt the main gas flow in the combustor instead of attaching to the liner wall. To ensure accurate positioning, the blow-off holes have to be machined separately from the impingement cooling holes. Separate hole machining operations require separate fixtures and set-ups, thereby generally increasing the cost of manufacturing the dome plate.
Furthermore, the axially facing lip on eyeletted dome plates must undergo a length trimming operation before the dome assembly can be fully assembled. This requirement further increases the cost of producing the dome plate.
Accordingly, there is a need for a low cost dome plate that retains the excellent performance of known dome plates and a method for making such a dome plate.
The above-mentioned need is met by the present invention which provides a method of making a dome plate. The method includes forming an annular body and forming a plurality of swirler openings in the annular body. Then, an array of impingement cooling holes and an array of blow-off holes are electrically discharge machined into the annular body adjacent to each swirler opening. For each one of the plurality of swirler openings, the corresponding array of impingement cooling holes and the corresponding array of blow-off holes are machined in a single electrical discharge machining operation. This results in an annular dome plate having radially outer and inner curved corners that define a single radius of curvature. The blow-off holes are located in at least one of the outer and inner curved corners.